The culture-based fisheries in small, farmer-managed reservoirs in twoProvinces of northern Vietnam: an evaluation based on three productioncycles

摘要

In this paper the results of a study conducted on the culture-based fisheries in small (ranging from 2 to 160 ha), farmer-managed reservoirs in YenBai and ThaiNguyen Provinces in the northern highland region of Vietnam, for the production cycles of 1997/98, 98/99 and 99/00 are presented. The small reservoirs are leased to small farmers by the provincial authorities for fishery activities, and all lessees adopt culture-based fisheries when fingerlings of grass carp (Ctenopharyngodon idella), silver carp (Hypophthahnichthys molitrix), bighead carp (Aristichthys nobilis), common carp (Cyprinus carpio) and mrigal (Cirrihinus mrigala) are stocked between March and mid-April each year and harvested, using large seine nets, after approximately 11-12 months. The mean yields from reservoirs in YenBai and ThaiNguyen Provinces in 97/98, 98/99 and 99/00 production cycles were 251, 332 and 253, and 331, 372 and 210 kg ha(-1) respectively. There were major differences in the fish productivity in the reservoirs in the two Provinces, and in a reservoir between culture cycles. The stocking strategies appeared to be rather ad hoc, being determined by the availability of seed stock and the financial status of the lessees. Accordingly, there was no apparent consistent trend in the improvement of yields from the culture-based fishery practice throughout the growth cycles. The fish yields in reservoirs in each Province were significantly related to reservoir area (exponentially) and to mean weight of stocked fish and conductivity (logarithmically). Of the stocked fish, the highest returns were obtained with mrigal and bighead carp. which collectively contributed > 50% to the harvest. The return from common carp was the lowest. The mean growth rate of grass carp (2.7 g day(-1)), followed by bighead carp (2.0 g day(-1)) was the highest in reservoirs in YenBai Province, bighead carp (4.0 g day(-1)) followed by grass carp (3.2 g day(-1)) was the highest in ThaiNguyen Province. The seed stocked on average accounted for 65% and 48% of the total operating costs in YenBai and ThaiNguyen Provinces, and the mean cost:benefit ratio of the culture-based fishery in the two Provinces was 0.35 and 0.37 respectively. The culture-based fishery on average contributed about 28% to the gross income of a farmer lessee.